Manufacture of fluorescent tubing



June 10, wlLLlAMS 2,421,975

MANUFACTURE OF FLUORESCENT TUBING Fi led March 19, 1945 Patented June10, 1947 UNITED STATES. PATENT OFFICE MANUFACTURE OF FLUORESGENT TUBINGRoscoel); Williams, Luisville,-Ky.

Application March 19, 1942; seriai No. 4793M 4 Claims.

The invention relates to tub'esfor fluorescent lighting and" thefabrication thereof.

The crystals in the" coating of fluorescent material on the innerperiphery of the glass tube for fluorescent lighting change the Wavelength of the light, part of which is ultra-violetjcreated by theelectrical discharge through the inert gas and mercury vapor to wavelengths of light which are perceptible by human vision", and producehighly efficient lighting, as a whole, but the fluorescent material,which has "a degree of opaqueness, toa degree restricts the visiblelight discharged from the tube One object of the invention is to providea tube for fluorescent lighting by which the light'-dis= charge isincreased in a controlled direction. This object is attained primarilyby relatively accomplished: by a controlledfiow of an abrasive, such. assuitable silica over a longitudinally extending' section or zcne" of*the glass tube after its entire periphery has. been coated with; thestandard or greater thickness of; fluorescent ma teri'al or thethickness desired: in the section 01! greater thickness. This method:lends itself to the reduction of. they thickness of the coating in onesection to the desired thinness for the controlcr light from the: tube.

Other objects" will appear from the: detailed. description of theinvention.

The invention consists in theseverar novel features which arehereinafter set forth and more; particularly defined by claims at theconclusion.

varying the thickness of the fluorescent coating in longitudinallyextending sections" or zones on the inner periphery; of the tube so thatone section will have a fluorescent coating oflesser thickness than theremaining section having a fluorescent coating of standardor greaterthickness. With these sections having coatings of differentthi'cknesathc sectiona reduced thickness will function to dischargelight at a higher rate than the other section and the section of thickercoating will function as areflector for the light transmitted throughthe section having the coating of reduced thickness; In this manner,the: discharge of light at thehigher rate is directi'onally controlledby the section with the coating of reduced thickness, without the use ofa reflector. By rotation of the tube on its axis and in thelamp-fixture, the direction of the light through the section having thereduced thickness of coating may be varied as desired. Some of the lightwhich passes directly through the coating of lesser thickness may,, adegree, be untransformed while the ultra-Violet light is ab sorbed bythe glass. or light is transformed the tube, the untransformed lightwhich'passes directly" through the coating of lesser thickness fiiaybe'clischarged'with a distinctive color of its own. 'Ihisdistin'ctive Whilethegreater amount j color added to the major portion of the trans- Inthe drawings:

Fig-L 1 a sectional view: illustrating the method: for reducing thethickness oi the: fluc resce'nt coating in -a section of the previouslycoated tube.-

Fig. Zis a transverse sectionof a tube with fluorescent coating ofdifferent thickness: on di'fe ferent sections of the tube.

3 is a section taken on. line 3 3't or Fig; 21. i 4 'i'sa Viewillustrating the tube with the discharge for controlling the flow ofabrasive throu h the time.

The improved fluorescent tubing is; illustrated irrFigs. 2 and 3- andcomprises a transparent glass tube 1' of usual wau'tnickness ans lengthfor" use in the fabrication ct tubular fluorescent lamps which areprovided with theusualend cans ahd electrical contacts and are adaptedto retain a suitable inert gas; as usuar ih theart} A coating 8(if-fluorescent chemical comainingpowder having crystalsof fluorescentminerals or chemicals and of thepredetermmeo or standard thickness nowused fluorescent lamps; extends around a sdtioirdr Z6119, f'tir exampleapproximately 24% or the inner eriphery; and from and: to" end or lsectibr i (if approximatei 1 20' or the inner perinhery-and extendingfrom eiid to end of the tubinga coating of lesser thickness than theportion 8. interior peripheral coating 8 of the tube may. also be madegreater that? standard th-i kI-iss to achieve a dire "cm-1 outputcf areater portion es the tdtal light emitted fi orii thetube 'llli section9 of the coating of the samefluorescent chemical with like powder ahdhas aiesser truer-nessthan the portions; or the thickness or: theflucrescent chemicar at a may bepractically nil. These coating"sectionsare formed by coating the entire periphery the tubing with thesame fluorescent chemical and powder of the thickness in the section 8of the coating and then removing a portion thereof from the inner faceof the coating to form the section 9 of lesser thickness. Thefluorescent coating 8 can be of standard or ordinary thickness 50 thatthe wave length of most of the light from the incandescent gas, a largepart of which is ultra-violet, will be changed by theprystals oi'thepowder in the fluorescent coating'jthe electrical discharge, the inertgas and mercury vapor, when the lamp is energized, to visible wavelengths of visible light, or of greater than standard thickness so thatmore of the last mentioned light is changed to visible light. Thiscoating, where it is 'of'greater or standard thickness, as in section 8,reduces the transparency throughout the area of the section to which itis applied. The area of the section 9 of the coating of reducedthicknessis provided to permit visible light to escape more freely from the. tubethan it does through th area having the thicker coating. As a result,the fluorescent material 8 of greater thickness functions not only totransform the ultra-violet light into visible light, but also to reflectthe visible light in the direction of section 9, and this visible lightcan be directionally controlled by the axial direction and the area ofthe coatin of reduced thickness.

The direction of this light passing through the section having thecoating of lesser thickness can be readily varied by rotation of thetube on its axis. Some of thelight that falls on the portion of the tubehaving the coating of lesser thickness may not be transformed. Most ofthis untransformed light is ultra-violet and is absorbed by the glassbut part of it is visible. The proportion of this visible anddirectionally controlled light may be controlled by the thickness of thecoating 9. This visible light directly from the incandescent gas whichescapes through the coating 9 has a distinctive color of its own. Thisdistinctive color, added to the translated light in the tube, changesthe color value to some extent of the lightemitted from the tube withcoating of lesser thickness and the color of the light when whitefluorescent tubes areusedis improved. Tubing coated as aforesaid withfluorescent material of different thickness makes it possible todirectionally control a large portion of the light emitted, results inan increase in light efliciency without the, use of a reflector, andimproves the color value of the emitted light.

The fluorescent material is of a loose and flocculent nature composedlargely of minute crystals of fluorescent material. This fluorescentmaterial transforms the ultra-violet light to visible and hence usefullight, but it possesses a degree of opaqueness. The present practice inthe art is to make the coating of optimum and uniform thickness so thatthe most lumens per watt of visible light are emitted by the tube whenenergized. An increase of the present standard thickness will cause moreof the ultra-violet light in the interior of the tube to be transformedto visible light, but less to be transmitted through the coating andglass. If the coating around the entire inner periphery of the tube isthinner than the standard, less light would be transformed, but morewould be transmitted. According to the present invention, the coatingcan be of increased thickness for the transformation of more of theultra-violet light and an increase of its reflecting power because asuificient amount of the coating is removed from the arcuate section 9for the emission and escape of the transformed and the increased flow oflight through the latter section. In carrying out the method ofproducing this tubing the apparatus illustrated in Fig. 1 may beadvantageously used. The tube I of glass is suspended at such an angleas to cause an abrasive to flow by gravity longitudinally over thecoating on the lower portion and through the entire length of the tube.A hopper I0 for the abrasive is stationarily supported in an elevatedtable II. The lower end of the hopper is connected by a section offlexible tubing I 2 to a flow control tube I3. The upper end of the tubeI is connected to the discharge end of the control tube by a flexiblehose section IS. The lower end of the suspended tube is supported by abar I1 which may be adjusted in steps over a support I8 to vary theangle of inclination of the tube I and correspondin-gly vary thevelocity of the abrasive through the tube I. The control tube I6 isprovided with a discharge orifice I9 which is shaped to direct theabrasive to the lower arc of, and to limit the rate of flow through, theglass tube I. The silica flows by gravity from hopper I I) to pipesection I2, control tube I3 and the orifice I9 to the bottom portion ofthe glass tube 1 and slides downwardly by gravity over the fluorescentcoating on the lower portion of the tube I. The orifice I9 and gravityconfine the abrasive to the section of the tubing 'I desired, and theorifice limits the flow into the tube. The abrasive in flowing over thecoating on the inner periphery of the glass tube I reduces the thicknessof the coating 9 of the section. The velocity and volume of the abrasiveflowing through the tube 1 may be readily controlled to reduce thethickness of the coating to the desired degree. The abrasive used mustflow freely through the orifice I9 and over the fluorescent coating onthe tube and must not leave any residue which will have a consequentialdetrimental reaction when the tube is fabricated into a lamp. Forinstance, the presence of iron in the abrasive is likely to have such adetrimental effect. An example of an abrasive which can be used incarrying out the invention consists of silica sand composed largely ofsilicon dioxide, which is substantially free from iron and othercontamination. The silica for this purpose must be composed of thefollowing:

Per cent 20 meshv .5 30 mesh v 32.2 40 mesh 62.8 50 mesh 4.0 '70 mesh0.5

mately 4 ounces of silica is placed in the hopper II] with an orificewhich will pass the charge in approximately seconds, will usuallyproduce the desired reduction in the thickness of the coating for astandard length of milimeter tubing. In practice it may be desirable toflow the silica over approximately of the area of the section 9 throughthe tube and then reverse the tube and flow silica through the other endof the tube positioned for the removal of the other half portion of saidsection. After the abrasive has been passed through the tubing a puff ofwarm air is forced through it to remove any loose fluorescent materialfrom the tube. This flow of silica will result in the thickness of thecoating being graduated between the sections so that there will be nosharp line of demarcation between them.

The abrasive material is discharged from the tube into a bin 20 and isprotected from outside contamination. The abrasive material may berepeatedly used until it becomes charged with the fluorescent materialto the extent that its abrasive and flow characteristics are changed.The fluorescent material can be washed and reclaimed from the silica ifdesired, and the cleaned and dried silica reused.

The method of removing the fluorescent coating may be advantageouslyused to remove substantially all of the fluorescent coating from anarrow section of the tubing, if that should be desired for specificuses.

The invention exemplifies a method of producing tubing coated withfluorescent material whereby the reduction in thickness of the coatingmay be accurately controlled and quickly and economically effected. Theinvention also exemplifles tubing for fluorescent lighting which isprovided with zones of fluorescent coating of the same material insections of different thickness for increasing the visible light emittedfrom the tubing for directional control.

The invention is not understood as restricted to the details set forthsince these may be modifled within the scope of the appended claimswithout departing from the spirit and scope of the invention.

Having thus described the invention What I claim as new and desire tosecure by Letters Patent is:

1. That improvement in making fluorescent lighting tubing whichcomprises: delivering into tubing, which is uniformly coated on itsinner periphery with fluorescent material of a predetermined thickness,abrasive material so it will flow over an arcuate portion of theperiphery of and longitudinally through the tubing until the coating insaid arcuate zone is reduced in thickness, for increased lightprojection therethrough of the light transformed and reflected by thecoating of predetermined thickness.

2. That improvement in making fluorescent lighting tubing whichcomprises: delivering into tubing, which is uniformly coated on itsinner periphery with fluorescent material of a predetermined thickness,abrasive material so it will flow by gravity over an arcuate portion ofthe periphery and longitudinally through the tubing until the thicknessof the coating in said arcuate zone is reduced in thickness, forincreased light projection therethrough of light transformed andreflected by the portion having the coating of predetermined thickness.

3. That improvement in making fluorescent lighting tubing whichcomprises: delivering into tubing, which is uniformly coated on itsinner periphery with fluorescent material of a predetermined thickness,abrasive material so it will flow at a controlled rate over an arcuateportion of the periphery and longitudinally through the tubing until thecoating in said arcuate zone is reduced in thickness, for increasedlight projection therethrough of light transformed and reflected by theportion having the coating of predetermined thickness.

4. That improvement in making fluorescent lighting tubing whichcomprises: delivering into tubing, which is uniformly coated on itsinner periphery with fluorescent material of a predetermined thickness,abrasive material so it will flow by gravity and at a controlled rateover an arcuate portion of the periphery and longitudinally through thetubing until the coating in said arcuate zone is reduced in thickness,for increased light projection therethrough of light transformed andreflected by the portion having the coating of predetermined thickness.

ROSCOE D. WILLIAMS.

REFERENCES CITED The following references are of record in the flle ofthis patent:

UNITED STATES PATENTS Number Name Date 2,318,060 Cortese May 4, 19432,179,288 Frech Nov. 7, 1939 2,238,784 Scott Apr. 15, 1941 2,196,058Coats Apr. 2, 1940 2,022,587 Cunningham Nov. 26, 1935 1,657,784Bergstrom Jan. 31, 1928 2,135,732 Randall et al Nov. 8, 1938 2,151,686Briefer Mar. 28, 1939

